Buggy code:
public class BcelShadow extends Shadow { private ShadowRange range ; private final BcelWorld world ; private final LazyMethodGen enclosingMethod ; private boolean fallsThrough ; public BcelShadow ( BcelWorld world , Kind kind , Member signature , LazyMethodGen enclosingMethod , BcelShadow enclosingShadow ) { } public BcelShadow copyInto ( LazyMethodGen recipient , BcelShadow enclosing ) { } public World getIWorld ( ) { } private void deleteNewAndDup ( ) { } private void retargetFrom ( InstructionHandle old , InstructionHandle fresh ) { } protected void prepareForMungers ( ) { } public ShadowRange getRange ( ) { } public void setRange ( ShadowRange range ) { } public int getSourceLine ( ) { } public TypeX getEnclosingType ( ) { } public LazyClassGen getEnclosingClass ( ) { } public BcelWorld getWorld ( ) { } public static BcelShadow makeConstructorExecution ( BcelWorld world , LazyMethodGen enclosingMethod , InstructionHandle justBeforeStart ) { } public static BcelShadow makeStaticInitialization ( BcelWorld world , LazyMethodGen enclosingMethod ) { } public static BcelShadow makeExceptionHandler ( BcelWorld world , ExceptionRange exceptionRange , LazyMethodGen enclosingMethod , InstructionHandle startOfHandler , BcelShadow enclosingShadow ) { } public static BcelShadow makeIfaceInitialization ( BcelWorld world , LazyMethodGen constructor , BcelShadow ifaceCExecShadow , Member interfaceConstructorSignature ) { } public static BcelShadow makeIfaceConstructorExecution ( BcelWorld world , LazyMethodGen constructor , InstructionHandle next , Member interfaceConstructorSignature ) { } public static BcelShadow makeUnfinishedInitialization ( BcelWorld world , LazyMethodGen constructor ) { } public static BcelShadow makeUnfinishedPreinitialization ( BcelWorld world , LazyMethodGen constructor ) { } public static BcelShadow makeMethodExecution ( BcelWorld world , LazyMethodGen enclosingMethod ) { } public static BcelShadow makeShadowForMethod ( BcelWorld world , LazyMethodGen enclosingMethod , Shadow . Kind kind , Member sig ) { } public static BcelShadow makeAdviceExecution ( BcelWorld world , LazyMethodGen enclosingMethod ) { } public static BcelShadow makeConstructorCall ( BcelWorld world , LazyMethodGen enclosingMethod , InstructionHandle callHandle , BcelShadow enclosingShadow ) { } public static BcelShadow makeMethodCall ( BcelWorld world , LazyMethodGen enclosingMethod , InstructionHandle callHandle , BcelShadow enclosingShadow ) { } public static BcelShadow makeShadowForMethodCall ( BcelWorld world , LazyMethodGen enclosingMethod , InstructionHandle callHandle , BcelShadow enclosingShadow , Kind kind , ResolvedMember sig ) { } public static BcelShadow makeFieldGet ( BcelWorld world , LazyMethodGen enclosingMethod , InstructionHandle getHandle , BcelShadow enclosingShadow ) { } public static BcelShadow makeFieldSet ( BcelWorld world , LazyMethodGen enclosingMethod , InstructionHandle setHandle , BcelShadow enclosingShadow ) { } public static void retargetAllBranches ( InstructionHandle from , InstructionHandle to ) { } private ObjectType getTargetBcelType ( ) { } private Type getArgBcelType ( int arg ) { } public boolean terminatesWithReturn ( ) { } public boolean arg0HoldsThis ( ) { } private BcelVar thisVar = null ; private BcelVar targetVar = null ; private BcelVar [ ] argVars = null ; public Var getThisVar ( ) { } public Var getTargetVar ( ) { } public Var getArgVar ( int i ) { } private BcelVar thisJoinPointVar = null ; private BcelVar thisJoinPointStaticPartVar = null ; private BcelVar thisEnclosingJoinPointStaticPartVar = null ; public final Var getThisJoinPointVar ( ) { } public final Var getThisJoinPointStaticPartVar ( ) { } public final Var getThisEnclosingJoinPointStaticPartVar ( ) { } public BcelVar getThisJoinPointBcelVar ( ) { } public BcelVar getThisJoinPointStaticPartBcelVar ( ) { } public BcelVar getThisEnclosingJoinPointStaticPartBcelVar ( ) { } public Member getEnclosingCodeSignature ( ) { } private InstructionList makeArgsObjectArray ( ) { } private void initializeThisVar ( ) { } public void initializeTargetVar ( ) { } public void initializeArgVars ( ) { } public void initializeForAroundClosure ( ) { } void weaveBefore ( BcelAdvice munger ) { } public void weaveAfter ( BcelAdvice munger ) { } public void weaveAfterReturning ( BcelAdvice munger ) { InstructionFactory fact = getFactory ( ) ; List returns = new ArrayList ( ) ; Instruction ret = null ; for ( InstructionHandle ih = range . getStart ( ) ; ih != ( range . getEnd ( ) ) ; ih = ih . getNext ( ) ) { if ( ( ih . getInstruction ( ) ) instanceof ReturnInstruction ) { returns . add ( ih ) ; <START_BUG> ret = ih . getInstruction ( ) . copy ( ) ; <END_BUG> } } InstructionList retList ; InstructionHandle afterAdvice ; if ( ret != null ) { retList = new InstructionList ( ret ) ; afterAdvice = retList . getStart ( ) ; } else { retList = new InstructionList ( fact . NOP ) ; afterAdvice = retList . getStart ( ) ; } InstructionList advice = new InstructionList ( ) ; BcelVar tempVar = null ; if ( munger . hasExtraParameter ( ) ) { TypeX tempVarType = getReturnType ( ) ; if ( tempVarType . equals ( VOID ) ) { tempVar = genTempVar ( OBJECT ) ; advice . append ( getFactory ( ) . ACONST_NULL ) ; tempVar . appendStore ( advice , getFactory ( ) ) ; } else { tempVar = genTempVar ( tempVarType ) ; advice . append ( getFactory ( ) . createDup ( tempVarType . getSize ( ) ) ) ; tempVar . appendStore ( advice , getFactory ( ) ) ; } } advice . append ( munger . getAdviceInstructions ( this , tempVar , afterAdvice ) ) ; if ( ret != null ) { InstructionHandle gotoTarget = advice . getStart ( ) ; for ( Iterator i = returns . iterator ( ) ; i . hasNext ( ) ; ) { InstructionHandle ih = ( ( InstructionHandle ) ( i . next ( ) ) ) ; Utility . replaceInstruction ( ih , fact . createBranchInstruction ( GOTO , gotoTarget ) , enclosingMethod ) ; } range . append ( advice ) ; range . append ( retList ) ; } else { range . append ( advice ) ; range . append ( retList ) ; } } public void weaveAfterThrowing ( BcelAdvice munger , TypeX catchType ) { }

Fix:
ret = Utility . copyInstruction ( ih . getInstruction ( ) ) ;